There are several known ways for discrete point-to-point wiring of components on printed circuit boards, backpanels or the like. By far the most common is the wire-wrap system. In this approach, a terminal, including either a socket or input/output (I/O) pin and a post, is fitted into a printed circuit board to form wiring points with the post projecting therefrom. An insulated wire is cut to length and each wire end is stripped of insulation exposing the conductor which is then wrapped around the terminal post. More than one level of wires may be wrapped on an individual post. Not only does this technique require considerable time for wrapping, unwrapping or modifying, but the three and four level wraps often require complicated programming and planning. Moreover, in the upper levels of a multi-wire-wrap termination, a problem in electrical impedance matching is encountered at short pulse rise times because of the physical distance the wires are located above the wiring board.
An alternative to the wire-wrap system which is intended as an improvement in providing greater economy of making connections on a wiring board is the "quick-connect" system which utilizes an insulation displacement technique. In this approach, a wire terminal including a socket or pin on one end and an insulation displacing contact portion on the other end, is mounted in a circuit board. The contact portion typically includes a pair of tines spaced by a slot for receiving an insulated wire. Interconnections are made by pushing the insulated wire into the slot such that the insulation is displaced and intimate contact is made directly with the wire conductor. More than one wire may be inserted into each slot and such a terminal may be utilized for both input and output purposes. Such insulation displacement terminals and interconnections are more fully described in two articles published by the Electronic Connector Study Group Inc. at the Fourteenth Annual Connectors and Interconnections Symposium Proceedings, Nov. 11 and 12, 1981, one article by Anthony G. Lubowe and C. Phillip Wu, Bell Telephone Laboratories, Inc., entitled "Quick Connect--A Circuit Pack Breadboarding Technique", pages 187-198, and the other by Don Fleming, Robinson Nugent, Inc., entitled "Quick Connect--A Point-To-Point Wiring System", pages 199-206.
One problem with the above insulation displacement approach is in the integrity of the electrical and mechanical connection, in particular with small diameter wires in the range of 30 gauge or finer. The contact tines are typically thin, of thickness about the diameter of the wire and, as such, the bearing surface on a wire is relatively small, resulting in the wire being insufficiently held for high contact reliability or mechanical strength. Another problem is the critical size of the wire slot which must be precisely maintained relative to wire diameter to provide a gas tight connection to the wire. Smooth transition regions at the slot edges, instead of sharp edges, are difficult to maintain in volume manufacturing and hence, increased cost and poorer performance result. Moreover, the stacking in one slot of multiple wires presents an additional problem in that an upper wire disturbs a lower one with an overall lessening in contact integrity.
Despite the new connection approaches, the wire-wrap system, even with its shortcomings, is still the standard of reliability by which other systems, especially mechanically crimped ones, are presently measured. As such, it is necessary to equal or exceed the electrical and mechanical reliability of wire wrap joints for a different termination system to be acceptable to the performance driven portions of the computer and telecommunication industries. These industries, spurred by the revolution in semiconductor technology and the development of very large scale integrated (VLSI) circuits, have great need for a discrete wiring system which at the same time offers high reliability, improved electrical impedance matching for the high speed signal pulses to and from VLSI circuits, much higher density of wiring, greater system versatility, and, of course, cost effectiveness. The present invention is intended to fill this need for an improved method of wire termination in a wiring system.
Those who have worked in the art of terminating fine wires, especially fine insulated wires in ranges from 30 gauge (10 mil copper) down to 42 gauge (2.5 mil copper) appreciate the problems involved in making reliable, low-cost terminations where literally billions of joints are involved. Among these problems are the low strength and small size of the wire (in some cases finer than human hair), the difficulty of maintaining dimensional control of very small contacts and, of course, precise control of the steps in terminating the wire. A highly reliable method of terminating fine insulated wire is desirably independent of manufacturing and of human variables. In other words, the wiring system should be inherently self-compensating for minor dimensional differences of wire and contact, for reasonable variations in applicator tooling, for differences in operator skill, and, most importantly, in the initial alignment of wire to contact.